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Cincinnati 12.5" Hydra(won't)shift

NCPatrol

Plastic
Joined
Jan 29, 2019
Hi all -

I have a 12.5x60 Hydrashift that I bought about a year ago from someone who had it in storage for about 15 years. When I got it I topped off the headstock hydraulic oil and tested it out to make sure everything worked before I tore in to the mostly cosmetic restoration. Everything seemed to shift like it should at that time.

Fast forward about a year, I finally buttoned it back up and got it wired last night and spun it up. The spindle IS spinning, but it is stuck in a single gear and I can not get it to shift. Absolutely nothing happens when I turn the shifter knob and stop/start/jog the clutch.

I can confirm that the pump is moving hydraulic fluid. (I had to do some work on the pump during the rebuild - new seals, had to re-key the shaft and pulley). I did clean the external filter but didn't mess with the internal one at the time.

I haven't checked pressure yet, but will probably throw together a gauge if I run out of other ideas.


I never removed the shifting assembly and didn't do anything to the interior workings on the headstock. I did poke around in there just seeing how things worked and I most likely did move some of the shifter "forks" around manually. My only theory at this point is that I moved something and it's out of sync somehow and doesn't know what to do....but I don't know how to get it back to where it wants to be or thinks it is.

Any pointers on where to troubleshoot this? I don't think I messed up anything major, but I'm really not sure where to begin...
 
My first guess would be that something is gummed up in the hydraulic circuits; it's a problem that others here have encountered. Contaminants and varnish can foul the piston bores and make them hard to shift. Lack of maintenance of the years can result in plugged hydraulic lines, strainers, or pump damage (your Hydrashift has two hydraulic pumps: the belt-driven one outside the headstock, and a second one inside the headstock driven by the internal "B" shaft).

You mentioned that you "topped off" the hydraulic oil a year ago. What oil did you use, and do you know what oil was in the headstock to begin with?

Before you tear into the hydraulics, I'd suggest taking off the headstock cover, and (with the motor off and electrics locked out) manually shifting the three forks through their full ranges of travel. You'll probably need to manually rotate the spindle to allow each gear combination to engage. Using a light and mechanic's mirror, try to verify that each gear set is properly engaged when the forks are in their detent positions.

When you power up the motor, can you hear the hydraulic pressure spool up? On my 12-1/2 Hydrashift, I can tell when the pressure is up far enough to shift gears.

When the spindle is turning in the one spindle speed that works, can you see oil flow in the sight glass on the front of the headstock? If not, then either the feed line to the sight glass is out of position or pinched off, or else the governor pump (the one that draws from the strainer inside the headstock) is not working or the strainer is plugged.

Even if you find the shift problem, testing the hydraulic system pressure per the manual is a good idea.
 
When I said I topped it off, I should have said I filled it up. It was completely empty when I got it. I actually found the fluid recommendations on another thread here when I did it. Pretty sure it was ISO 30, but I'd have to go look at the bucket. The machine worked perfectly back then though.

I know for sure that the pump is moving fluid. I have it on a VFD so I can run it a little slower with the top off and see the fluid moving and bubbling up out of the port on the back left corner of the assembly. With the cover on and running full speed, it still won't shift. I didn't run it enough to know what it should sound like when it's loaded up though.

I can move all the the forks through their ranges by hand with the motor off. No signs of varnish or anything on them that would prevent them from moving. I tried just about every speed and could always get the spindle to spin at that speed, still no shifting. I was hoping there was a specific place they all had to be to get it to reset and know what it was supposed to be doing.


I guess I need to get to that strainer and make sure it clean and then look in to the governor pump next.

hydra.jpg
 
Most users seem to recommend Mobile DTE Light for the Hydrashift headstock. I've been using it for several years with good results.

There's no specific position that the forks must be in to "reset", but the manual does describe where the shift drum should be when re-assembling everything.

The governor pump pressure (or more precisely, the lack of pressure) allows the shifts to occur. The shift body interprets the lack of governor pump pressure as a signal that the headstock gear shafts have stopped rotating, and it's safe to shift gears. Sounds like either residual pressure in the governor pump circuit, or something in the shift body that's hanging up and fooling the mechanism.

The governor pump strainer cannot be removed without some disassembly of the headstock gearing and shafts, so the manual describes a reverse flushing procedure. The governor pump itself can be removed from outside of the headstock. If you do this, be careful to reassemble the pump correctly (it's an ingenious design that pumps the same direction regardless of the rotation direction of the input shaft), and install it correctly into the headstock.
 
Finally got a pressure gauge rigged up and, assuming I'm on the right port, I have zero pressure on the gauge.

There is oil flowing through the head stock, but I'm assuming it's all from the external pump and the governor pump is my problem.


hydra3.jpg
hydra4.jpg
 
Thought I'd follow this one up since I'm not afraid to admit my stupidity....


Finally had a chance to really dig in to this thing. The lack of hydro pressure/flow was bugging me and after staring it at again for a solid 5 minutes, I realized I had not been "reading" the hydraulic system correctly. The flow that I was seeing that I though was from the external pump, was actually from the governor pump. Turns out the external pump wasn't pumping at all. When I pulled the upper line to check, I found that it was actually sucking!

Still not entirely sure how I managed that as the fittings to the hard lines could only work one way and I never touched those. The only thing I can think is that when I reassembled the pump I got the two halves of the pump body rotated 180 degrees from where the should have been, effectively reversing the flow. I didn't think about this until I got done switching the fittings....it would have been a lot easier to just spin one side of the pump 180.

But, I did swap the fittings and flipped the entire pump 180 degrees and now I have full hydraulic flow and she's shifting. All gears seem to work but I was occasionally getting a little grind in the upper speeds. I suspect it's because I'm running it off a sketch VFD and I couldn't get it quite up to a full 60hz without the VFD shutting down. I'm getting ready to move to a new place with a bigger shop so I'll get the fine details worked out and get it properly powered when I'm settled in.
 








 
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